1. Field of the Invention
The present invention relates to a protection circuit and a control circuit each for preventing failure or malfunction of a device due to abnormal current.
2. Description of the Related Art
In order to prevent failure or malfunction of a device due to abnormal current, there is provided a protection circuit that suppresses an inrush current, which occurs when the power is turned on, and protects an electronic circuit from reverse connection of a power source. In this respect, the reverse connection of the power source means that the power source is erroneously connected to the electronic circuit with reverse polarity. P-channel MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistor) are often used for this protection circuit.
In recent years, there has been increased demand for a protection function for preventing failure or malfunction of a device due to abnormal current to a control circuit of a device such as a general-purpose fan motor as well as a communication device and a server. Thus, the protection function is required as standard to be embedded in an IC motor driver, thereby reducing external components to make the control circuit compact and reduce cost thereof.
JP-A-2006-033836 describes a problem to be solved Where “a hot swap circuit system of a fan module capable of reducing manufacturing costs of the system, and for making the system to be operable in a condition of large current and voltage while improving stability of the system” is provided. This publication describes a solution where “the hot swap circuit system of the fan module includes a soft: start circuit module for powering a power source of the fan module when the fan module is made hot plug to an application system. The soft start circuit module has a capacitor and a field effect transistor wherein the capacitor discharges potential when an input voltage of the soft start circuit module is switched from a non-zero value to a zero value, and the field effect transistor goes to an off-state when the input voltage of the soft start circuit module is switched from the non-zero value to the zero value”.
The hot swap circuit described in JP-A-2006-033836 uses a P-channel MOSFET. However, as compared with an N-channel MOSFET, a chip size of a P-channel MOSFET is larger, more expensive and difficult to make in a fabrication process. For these reasons, in recent years, the number of suppliers of P-channel MOSFETs has decreased and hence product lines have also decreased. Thus, the availability of these MOSFETs in the future is questionable. As a result, a protection circuit capable of using an N-channel MOSFET is desired.
Further, the hot swap circuit described in IP-A-2006-33836 does not have the function of protecting an electronic circuit from the reverse connection of the power source.